1. Field of the Invention
The present invention relates to a generator driving apparatus for driving a motor-generator, and more particularly to a generator driving apparatus which can regenerate energy stored by the motor-generator to an electric power system when the motor-generator is coming to a stop.
2. Description of Related Art
FIG. 1 is a circuit diagram showing a conventional generator driving apparatus for driving a flywheel generator, in which P designates an electric power system for supplying 3-phase electric power, and reference numerals 1a, 1b, 1c and 1d designate switches. The electric power system P is connected with an induction motor 2 through the switch 1d, and a motor-generator 3 is connected to the induction motor 2 driven by a Sherbius system 8 to be discussed below.
A flywheel 4 rotatable together with the motor-generator 3 is connected thereto and an exciter 5 is magnetically connected therewith, the motor-generator 3, flywheel 4 and exciter 5, comprising the flywheel generator. Furthermore, an intermittent load 6 is connected to the motor-generator 3.
A liquid resistor 7 is connected to the induction motor 2 through the switch 1c, which comprises a resistor for generating Joule heat and a liquid for cooling the resistor, the induction motor 2 being provided with a rotation detector (not shown).
The Sherbius system 8 is connected with the electric power system P through the switch 1a, has a rectifier transformer 8a connected to the switch 1a at the primary windings thereof, a thyristor rectifier 8b connected to the secondary windings of the rectifier transformer 8a and a diode rectifier 8d connected in inverse-parallel thereto through a DC circuit breaker 8c, and is connected to the induction motor 2 through the switch 1b. The Sherbius system 8, induction motor 2 and liquid resistor 7, comprise a driving apparatus for controlling the number of rotations of the motor-generator 3.
Next, an explanation will be given of the operation of the generator driving apparatus shown in FIG. 1. The driving of the motor-generator 3 is controlled by the induction motor 2 and liquid resistor 7 in a range from zero to the lowest usable number of rotations, and by the Sherbius system 8 and induction motor 2 in a range from the lowest to the highest usable number of rotations.
When the motor-generator 3 is started, in the range from zero to the lowest usable number of rotations thereof, the switch 1d is closed and switches 1a, 1b and 1c are open, so that the electric power system P supplies electric power to the induction motor 2 so as to drive the induction motor 2 and the motor-generator 3 is accelerated thereby. Thereafter, the switches 1a and 1b are closed and switches 1c and 1d are opened to switch the driving control until the number of rotations of the motor-generator 3 reaches its rated value (under the maximum number of rotations). The electric power system P supplies the electric power to the induction motor 2 through the Sherbius system 8 so as to drive the induction motor 2 so that the motor-generator 3 is accelerated by the Sherbius system 8 and induction motor 2.
The motor-generator 3 driven at its rated number of rotations under the control of the Sherbius system 8 feeds electric power to the intermittent load 6, which consumes energy to lower the number of rotations of the motor-generator 3 and the induction motor 2 coaxially connected thereto. When the rotation detector (not shown) detects a reduction in the number of rotations of the induction motor 2, the Sherbius system 8 accelerates the induction motor 2 while no electric power is fed to the intermittent load 6, thereby returning the number of rotations of the induction motor 2 to a desired rated number of rotations.
When the motor-generator 3 is stopped, the Sherbius system 8 and induction motor 2 are used to decelerate the motor-generator 3 until the number of rotations thereof reaches the lowest usable number of rotations. When this point is reached, the switch 1b is opened and switch 1c is closed so as to switch driving control by the Sherbius system 8 to the liquid resistor 7. Energy stored by the rotation of the motor-generator 3 and flywheel 4 is consumed as Joule heat by the liquid resistor 7, the motor-generator 3 continuing speed reduction to stop at last.
The conventional generator driving apparatus, as above-mentioned, comprises the Sherbius system 8, liquid resistor 7 and induction motor 2. Accordingly, when the driving of the motor-generator 3 is controlled, a problem is created in that the control must be executed by switching the Sherbius system 8 and liquid resistor 7. Also, when the motor-generator 3 is decelerated to a stop, since the stored energy is consumed by the liquid resistor 7, an electric power loss occurs.